The present invention relates to a refrigerant circuit and compressor that are incorporated in vehicle air conditioners
A refrigerant circuit includes a compressor and an expansion valve. The outlet of the compressor is connected with the expansion valve by a high pressure conduit. The high pressure conduit includes a condenser. The inlet of the compressor is connected with the expansion valve by a low pressure conduit. The low pressure conduit includes an evaporator. The compressor compresses refrigerant gas and sends it to the condenser. The condenser receives high pressure, high temperature refrigerant gas from the compressor. The condenser then cools and liquefies the gas. The liquefied refrigerant is expanded by the expansion valve and is turned into mist. The refrigerant mist is drawn to the evaporator. In the evaporator, heat exchange takes place between the refrigerant mist and the air in a passenger compartment, and vaporizes the mist. At this time, the heat of vaporization cools the air. The cooled air is then used to cool the passenger compartment.
In prior art refrigerant circuits, heat exchangers such as condensers and evaporators have a small heat capacity and thus are easily heated. Contrarily, the compressor has relatively great heat capacity and is not easily heated. Therefore, when the compressor is stopped for an extended period, a change in the ambient temperature produces a temperature difference between the compressor and the heat exchangers. The temperature difference results in a pressure difference between the compressor and the heat exchangers. The pressure difference causes liquefied refrigerant in the heat exchangers to enter the compressor and to get mixed with lubricant oil stored in the compressor. When operation of the compressor is resumed, the liquefied refrigerant in the compressor foams up and quickly flows back to the refrigerant circuit. This also removes the oil mixed with the liquefied refrigerant from the compressor. Thus, lubrication of the compressor may become insufficient. In order to solve this problem, some prior art refrigerant circuits have a check valve in the vicinity of the compressor outlet for preventing liquefied refrigerant from entering the compressor.
However, a typical refrigerant circuit includes a relief valve to discharge abnormally high pressure from the refrigerant circuit. The relief valve is located in the high pressure conduit in the vicinity of the condenser. If such a circuit is provided with a check valve in the vicinity of the outlet of the compressor, a malfunction of the check valve can cause the pressure in the compressor to be abnormally high.